A wide variety of machines, notably heavy-duty mobile machines such as construction, agricultural and transport machines utilize on-board compressed air for various purposes. Compressed air may be used for brake or implement system actuation, to power certain tools, for debris cleaning, and myriad other uses. Relatively recently, compressed air has begun to be used in conjunction with exhaust aftertreatment elements, in particular for compression ignition diesel engines.
One example of an exhaust aftertreatment element utilizing compressed air is known in the art as a urea injection module. Urea acts as a reducing agent for NOx in engine exhaust. It is typically necessary to provide some means for injecting the urea into an engine exhaust stream, and compressed air has been found to be well suited for this purpose. Many machines are equipped with a stand alone on-board air compressor, driven parasitically off the engine or electrically from a generator or alternator. More recently, compressed air has been provided from a compressor of a turbocharger coupled with the engine. In such systems, use of a separate air compressor may be dispensed with, so long as adequate compressed air from the turbocharger compressor is available.
U.S. Pat. No. 6,167,698 to King et al. is directed to an exhaust gas purification system for a lean burn engine. In the strategy described by King et al., a system is provided having a reservoir for storing compressed air received from a turbocharger. A reductant injector is in fluid communication with a reductant supply, and may be actuated to inject a quantity of reductant into a mixing chamber. The mixing chamber is configured for introducing air and reductant mixture into the engine's exhaust gas flow upstream of a NOx conversion catalyst. While the strategy disclosed by King et al. may have certain applications, there is always room for improvement. Under certain operating conditions it may be difficult for a standard turbocharger to accommodate the demand for compressed air in the King et al. approach due to the design of the system.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.